Known in the art is an acoustic wave element having a piezoelectric substrate and an IDT (InterDigital Transducer) electrode (excitation electrode) provided on a major surface of the piezoelectric substrate. The IDT electrode has a pair of comb-shaped electrodes. Each comb-shaped electrode has for example a bus bar extending in the propagation direction of the acoustic wave and a plurality of electrode fingers extending from the bus bar in a direction perpendicular to the propagation direction of the acoustic wave. The pair of comb-shaped electrodes are arranged so that their plurality of electrode fingers mesh with each other (so that they intersect with each other). Further, there is also known an IDT electrode which further has dummy electrodes each extending from one of the bus bars to the other bus bar side, wherein the tips face the tips of the plurality of electrode fingers extending from the other bus bar through gaps.
Further, it is also known that a so-called transverse mode spurious wave sometimes occurs in the impedance characteristic in an acoustic wave element utilizing a quartz substrate, LiNbO3 substrate, or the like as the piezoelectric substrate.
Patent Literature 1 discloses that a transverse mode spurious wave can be suppressed by obliquely inclining an intersection part (range where a plurality of electrode fingers of a pair of comb-shaped electrodes intersect with each other) relative to the propagation direction of the SAW in an IDT electrode having dummy electrodes.
Patent Literature 2 discloses that an IDT electrode having dummy electrodes wherein a transverse mode spurious wave can be suppressed by making mutually facing edge parts of two bus bars incline relative to the propagation direction. Further, in Patent Literature 2, a plurality of acoustic wave elements are experimentally produced by changing their inclination angles. The preferred inclination angles are regarded to be 18° to 72° based on the evaluation results. Further, Patent Literature 2 also disclose an IDT electrode in its FIG. 11 wherein the intersection part is formed obliquely relative to the propagation direction in the same way as Patent Literature 1.
When the intersection part is inclined relative to the propagation direction as in Patent Literature 1 and Patent Literature 2, the gaps between the tips of the plurality of electrode fingers and the tips of the dummy electrodes are arranged with a slant relative to the propagation direction of the acoustic wave as well, therefore the gaps end up entering into the range where the acoustic wave is originally going to propagate. Accordingly, the acoustic wave is apt to be scattered across the gaps, and consequently propagation loss is apt to occur. In both of Patent Literature 1 and Patent Literature 2, attention is paid to suppression of a spurious wave though no attention is paid to such propagation loss.
Further, in Patent Literature 2, nothing at all is mentioned about the shape of the intersection part (inclination angle of arrangement of the plurality of gaps) in trial manufacture and evaluation while changing the inclination angle of the edge part of the bus bar. Further, as deduced from a comparison of FIG. 3 and FIG. 5 in Patent Literature 2, in trial manufactures, the shape of the intersection part is a square as it is. That is, Patent Literature 2 shows no finding about the preferred range of numerical values for the inclination angle of the arrangement of the plurality of gaps.
Accordingly, provision of an acoustic wave element and acoustic wave device capable of suppressing propagation loss is desired.